Positive-displacement machine with reciprocating and rotating pistons, particularly four-stroke engine

ABSTRACT

Four elements (9a, 9b, 11a, 11b) are mutually articulated as a parallelogram deformable according to four parallel axes (A1, . . . A4). A crank (31) causes a circular motion of a first co-ordination axis (K1) connected to one (9a) of the elements. Another element (11b) is articulated to the frame along a second co-ordination axis (K2). A variable volume chamber (17) is defined between the cylindrical surfaces (S1, . . . S4) whose axes (C1, . . . C4) intersect the longitudinal axes (Da, Db) of the first elements (9a, 9b). Distribution orifices (19, 21) are selectively open and obturated by the elements as a function of the angular position of the crank (31). A sparking-plug is provided. Each first element (9a, 9b) carries two cylindrical convex surfaces (S1, S2; S3, S4) the rigidely interconnected. Each cylindrical surface is in dynamic sealing relationship with a cylindrical surface belonging to the other element and whose axis (C1, . . . C4) instersects a same line (L14, L23) parallel to the longitudinal directions (Ea, Eb) of the second elements (11a, 11b). Utilization for easily constructing a rapid machine of the type four-stroke one-cycle per revolution and low relative speed of the dynamic sealing lines.

The present invention concerns a positive-displacement machine in whichreciprocating and rotating pistons define between them a variablevolume-chamber.

The FR-A-2 651 019 describes a positive-displacement machine comprisingfour elements connected as a deformable parallelogram. Each elementcomprises a convex cylindrical surface and a concave cylindricalsurface, each centered on one of the articulation axes of the elementand co-operating in a sealed manner with the concave cylindrical surfaceof one of the neighbouring elements and with the convex cylindricalsurface of the other neighbouring element respectively. One of thearticulation axes of the parallelogram is fixed, and the opposite axisis driven in a circular motion. This simultaneously causes a variationin the angles at the apex of the parallelogram and an oscillation of theparallelogram around its fixed axis. The variation in the angles of theparallelogram causes the volume of a chamber defined between the fourconvex cylindrical surfaces to vary. The oscillation around the fixedaxis enables this chamber to communicate selectively with an inlet portand an exhaust port. A thermal engine is thus created which performs thefour strokes (inlet, compression, explosion, exhaust) in a singlerevolution of a crank.

This machine has the drawback of being relatively big for a givendisplacement capacity, and of failing to enable very high compressionratios.

The construction of each element requires considerable precision for ahigh-quality seal to be achieved without mechanical friction becomingprohibitive.

The object of this invention is to offer a positive-displacement machinewhich overcomes these drawbacks.

The invention is thus directed to a positive-displacement machinecomprising, between two flat, parallel faces facing one another, twofirst opposing elements articulated to two second opposing elementsaround four articulation axes perpendicular to the said faces andarranged at the four apexes of a parallelogram each side of whichconstitutes the longitudinal axis of a respective one of the first andsecond elements, the elements supporting four convex cylindrical wallswhich between them define a variable-volume chamber, the longitudinalaxis of each first element being intersected by the axes of tworespective convex cylindrical walls, two lines running in the samedirection as the axes of the second elements each being intersected bythe axes of two respective convex cylindrical walls, the machine alsocomprising means of co-ordination connected to two of the elements alongtwo co-ordination axes, the means of co-ordination comprising a cranktype system connected to a drive shaft and to one of these two elementsto make the parallelogram oscillate between the flat faces and at thesame time cause its angles at the apexes and consequently the volume ofthe chamber to vary, distribution ports being located on one at least ofthe opposing flat faces to cause the chamber to communicate selectivelywith an inlet and exhaust depending on the angular position of thecrank.

According to the invention, the machine is characterised in that eachfirst element rigidly supports the two convex cylindrical walls whoseaxes intersect the longitudinal axis of the said first element, in thateach convex cylindrical wall forms with the convex cylindrical wallintersecting the same line a pair of cylindrical walls belonging todifferent first elements, in that each first element has closure meansextending between its two convex cylindrical walls, and in that themachine comprises means of dynamic sealing between the convexcylindrical walls of a same pair.

The main function of the second elements is to maintain a constantdistance between the centers of the convex cylindrical walls of the samepair.

In other words, everything occurs as if a deformable parallelogram wouldconnect the four axes of the four convex cylindrical walls. Thus thedistance between the convex cylindrical walls of the same pair is alwaysthe same, whatever the configuration of the deformable parallelogram.This makes it possible to provide dynamic means of sealing, between theconvex cylindrical walls of the same pair, even though such walls canmove in relation to each other. The convex cylindrical walls ofdifferent pairs and which are adjacent to each other around theperiphery of the parallelogram are fixed in relation to each other sincethey are supported by the same first element, and it is therefore easyto achieve a sealed connection between them using the means of sealingclosure, which may be of a static type.

Between the four convex cylindrical walls a chamber is thus definedwhose periphery is closed in an essentially sealed manner and whosevolume varies depending on the configuration of the parallelogram.

Preferably, the positive-displacement machine according to the inventionis designed to operate as a four-stroke thermal engine, and inparticular comprises means to initiate combustion positioned tocorrespond with the chamber at least when the latter is in a firstminimal-volume position.

The machine according to the invention, like the above-discussed priorart machine, performs the four strokes in a single turn of a crank. Butits size is reduced and there are only two dynamic seals around thechamber, between the convex cylindrical walls of the same pair.Furthermore, these seals can be reduced to a single tangential contactbetween convex cylindrical walls, which is a particularly simplesolution and extremely reliable even at very high speeds. In particular,this type of proximity relation is not apt to cause seizing.Furthermore, the relative speed between the convex cylindrical walls ofthe same pair is particularly low, for a given speed of rotation of thecrank.

It is also possible to interpose between the convex cylindrical walls ofthe same pair a sealing element such as a generally biconcave-shapedfloating bar, or even a sealing body fixed to a second elementarticulated to the first elements around two articulation axescorresponding with the axes of the cylindrical walls of the pair inquestion.

Other details and advantages of the invention will emerge more clearlyfrom the following description, relating to examples which are in no wayrestrictive.

In the attached drawings:

FIG. 1 is a view of an elemental machine according to the invention,along I--I of FIG. 3;

FIG. 2 is a partial sectional view along II--II of FIG. 1;

FIG. 3 is a sectional view of the machine along line III--III of FIG. 1;

FIGS. 4, 5 and 7 are similar views to FIG. 1, but showing the machine atthree successive stages of its operation;

FIG. 6 is a diagrammatic view showing one of the chamber'smaximum-volume positions;

FIGS. 8 and 9 are views corresponding to FIGS. 5 and 1 respectively, butwith a different compression ratio adjustment;

FIG. 10 is a similar view to FIG. 4 but corresponding to a modifiedembodiment;

FIGS. 11 to 13 are views similar to the bottom of FIGS. 1, 10 and 5respectively, but relating to a second modified embodiment;

FIG. 14 is a schematic view of the inner face of a head 4 according to athird modified embodiment;

FIG. 15 is a partial sectional view of the machine along line XV--XV ofFIG. 14;

FIG. 16 is a view similar to FIG. 4 but concerning a fourth modifiedembodiment;

FIGS. 17 and 18 are two schematic views of a fifth modified embodimentof the invention in a maximum-volume position and minimum-volumeposition respectively;

FIG. 19 is a perspective view of a sealing body for the machine in FIGS.17 and 18;

FIG. 20 is a schematic view of the four elements of a sixth embodimentof the invention;

FIG. 21 is a view similar to FIG. 5, but relating to another embodiment;

FIG. 22 is a large-scale detail of FIG. 21;

FIG. 23 is an exploded perspective view of one of the first elements inFIG. 21, and some of its parts, with sectional and cutaway sections;

FIG. 24 is a sectional view along XXIV--XXIV of FIG. 21;

FIG. 25 is a partial view of another embodiment of the first element;and

FIG. 26 is a sectional view of the first element along linesXXVIa--XXVIa at the top of the Figure and XXVIb--XXVIb at the bottom ofthe Figure.

We shall now describe with reference to FIGS. 1 and 2, and also to thetop of FIG. 3, a first example of the elemental machine according to theinvention.

An actual machine may comprise a single elemental machine or severalelemental machines, for example two elemental machines 1 as shown inFIG. 3, where the elemental machine at the bottom corresponds to amodified embodiment which shall be described in detail later.

As shown at the top of FIG. 3, the machine comprises a housing 2 whichdefines for each elemental machine two flat parallel faces 3a and 3bfacing each other. Flat faces 3a are defined at least in part by twoopposing heads of housing 2, whereas the two faces 3b are formed by twoopposing faces of an intermediate partition 6 located at an equaldistance between the two faces 3a. The distance between each head 4 andintermediate partition 6 is defined by a respective peripheral wall 7.

A part 3c of flat face 3a of the elemental machine at the top of FIG. 3is defined by a turret 8, in the form of a plate, which is mountedrotationally in a suitable recess in corresponding head 4, for reasonswhich will emerge later.

Heads 4, intermediate partition 6 and peripheral walls 7 together form aframework for the machine. Turret 8 is movable in relation to thisframework but, as an element defining the volumes inside the machine, isdeemed to belong to housing 2.

As FIG. 1 shows, each elemental machine 1 comprises, between flat faces3a and 3b, two first opposing elements 9a and 9b, and two secondopposing elements 11a and 11b.

Each first element 9a or 9b is articulated to the two second elements11a and 11b around two separate articulation axes. There are thereforefour separate articulation axes A1, A2, A3, A4 which are all parallel toeach other and perpendicular to flat faces 3a and 3b.

These four axes A1, A2, A3, A4 are located at the four apexes of aparallelogram. The longitudinal axis of each element 9a, 9b, 11a and 11bmeans the side of the parallelogram Da, Db, Ea, Eb respectively, whichjoins the two articulation axes of the element in question, for examplethe articulation axes A1 and A2 for the first element 9a having thelongitudinal axis Da.

FIG. 2 shows the structure of the articulation of axis A4 betweenelements 9b and 11b. The end of first element 9b has two parallel ears12, forming a fork, between which a single ear 13 of second element 11bis engaged. A tubular pin 14 is fitted through the two ears 12 and ear13 to achieve the articulated connection.

Each first element 9a or 9b has, on its side turned towards the otherfirst element, two convex cylindrical walls S1, S2 and S3, S4respectively defined by inserted linings 16.

Axis C1, C2, C3 or C4 of each cylindrical wall S1, S2, S3 or S4intersects longitudinal axis Da or Db of the first element 9a or 9b withwhich the cylindrical wall is integral.

Furthermore, each cylindrical wall S1-S4, forms with a cylindrical wallof the other first element, a pair of cylindrical walls whose axesintersect the same line L14 or L23 parallel to longitudinal axes Ea andEb of the second elements 11a and 11b. Thus, cylindrical walls S1 and S4together form a pair whose axes C1 and C4 intersect the same line L14parallel to axes Ea and Eb, and similarly, walls S2 and S3 form a pairwhose axes C2 and C3 intersect the same line L23 parallel tolongitudinal axes Ea and Eb.

It will therefore appear that axes C1, C2, C3, C4 are at the four apexesof a second parallelogram whose sides C1C2 and C3C4 are alwaysindistinguishable from longitudinal axes Da and Db of the first elements9a and 9b and whose sides C1C4 and C2C3 (Lines L14 and L23) are alwaysparallel to axes Ea and Eb.

In the example, axes C1 and C2 are located between axes A1 and A2 of thecorresponding first element 9a, and axes C3 and C4 are located betweenaxes A3 and A4 of the first corresponding element 9b. This is anadvantageous practical arrangement with all the cylindrical walls S1-S4being located between the second elements 11a and 11b.

In the example shown, each second element 11a, 11b has a curved shapewhich is concave towards the inside of the parallelogram in order,particularly in the extreme position shown in FIG. 1, to marry up withthe contour of cylindrical wall S1 or S3 respectively which is thenclosest. Size is thus reduced to a minimum. This also applies to wallsS2 and S4 in another extreme position shown in FIG. 5.

The four elements 9a, 9b, 11a, 11b can move in relation to each other,starting from the extreme position shown in FIG. 1 and may thus assumedifferent attitudes, some of which are shown in FIGS. 4, 5, 6(schematically) and 7.

In the situation shown in FIG. 4, a chamber 17 has formed between thetwo first elements 9a and 9b. Chamber 17 is delimited by that part ofeach cylindrical wall S1-S4 which is located inside parallelogram C1,C2, C3, C4, as well as by closure means formed by two concavecylindrical surfaces 18 each rigidly supported by one of the firstelements 9a and 9b and connecting the two convex cylindrical walls S1and S2 or S3 and S4 respectively of the first element in question. Eachconcave cylindrical surface is complementary to each of the convexcylindrical walls of the other first element. Thus, in the attitudeshown in FIG. 1, cylindrical wall S2 of first element 9a fits intoconcave surface 19 of first element 9b, and cylindrical wall S4 of firstelement 9b fits into concave surface 18 of first element 9a, whichreduces the chamber to a volume which is essentially zero. The situationshown in FIG. 1 corresponds to the end of explosion or start of inlet.Reducing the volume of the chamber to zero at this stage of the cyclemakes it possible to evacuate the exhaust gases completely and toseparate the latter perfectly from the gases which will just be admittedfor the next engine cycle.

Returning to FIG. 4, chamber 17 is also closed by dynamic sealing means.In the example these dynamic sealing means consist in a selecteddimension: radii R1, R2, R3, R4 of convex cylindrical walls S1-4 areselected so that the sum of the cylindrical wall radii of the same pairis equal to the distance between the axes of the cylindrical surfaces ofthe same pair.

In the example, radii R1-R4 are equal to each other and equal to halfthe distance between axes C1 and C4 or between axes C2 and C3. Thus thecylindrical walls of the same pair, S1 and S4 or S2 and S3, arepermanently in tangential proximity which ensures an essentially sealedclosure of chamber 17.

Furthermore, chamber 17 is closed by flat parallel faces 3a and 3b (FIG.3), except in certain attitudes (FIGS. 4 and 6) where chamber 17communicates with an inlet port 19 (FIG. 4) or with an exhaust port 21(FIG. 6). The inlet 19 and exhaust 21 ports are made through rotaryturret 8. They cause chamber 17 to communicate selectively with an inlet22, such as a carburetor and an exhaust 23 respectively.

Turret 8 has a central hole 24 into which the electrodes of spark-plug25 screwed into head 4 project. Central hole 24 also causes chamber 17to communicate with a back-pressure space 26 which is between a backface of turret 8 and head 4. A gasket 27 peripherally delimitsback-pressure space 26 and separates it from inlet 19 and exhaust 21ports located radially outside. The periphery of rotary turret 8completely surrounds chamber 17 in all the attitudes of the fourelements 9a and 9b and 11a and 11b. Thus, the clearance around turret 8can never be a leakage line for chamber 17. The pressure in chamber 17,particularly when the former is high, creates in back-pressure space 26a back-pressure which pushes turret 8 against first elements 9a, 9b andpresses them against flat face 3b. A sufficiently sealed contact is thusensured between elements 9a, 9b and each of flat faces 3a and 3b allaround chamber 17 whatever its configuration. In order for theback-pressure in space 26 to generate a pressing force greater than thepressure in chamber 17, the area delimited by gasket 27 around hole 24simply needs to be greater than the greatest area that chamber 17 canhave when the latter is under pressure, i.e. essentially during thecompression and explosion strokes.

As previously stated, the situation shown in FIG. 1 is minimum-volumesituation corresponding to the end of exhaust and start of inlet.

In the situation shown in FIG. 4, chamber 17 has become bigger overinlet port 19. Consequently, the chamber has taken in fresh gas.

In the situation shown in FIG. 5 corresponding to the end of compressionand start of combustion, we are again in a minimum-volume situation inwhich chamber 17 is isolated from inlet 19 and exhaust 21 ports andcommunicates with central hole 24 which accomodates the spark-plugelectrodes. We can see that in this minimum-volume situation angles Q1and Q3 of the parallelogram adjacent to axes A1 and A3, which were acutein the end of exhaust situation (FIG. 1) have become obtuse in the startof combustion situation (FIG. 5), and conversely as regards angles Q2and Q4 adjacent to axes A2 and A4.

Chamber 17 then enlarges again (FIG. 6) to perform an engine stroke orgas explosion stroke, then communicates with exhaust port 21 until itsvolume becomes zero again as shown in FIG. 1.

We can see that the situations in FIG. 4 (inlet) and FIG. 5 (explosion)correspond to essentially identical attitudes of the four elements 9a,9b, 11a and 11b in relation to each other. The fact that chamber 17communicates with inlet port 19 in the situation shown in FIG. 4 andwith exhaust port 21 in the situation shown in FIG. 5 is due to the factthat the four-element assembly 9a, 9b, 11a, 11b is not in the same placein the space defined by the inner peripheral face of peripheral wall 7.The movements of elements 9a, 9b, 11a, 11b in relation to each other aswell as the movements of the assembly that they form inside peripheralwall 7 are defined by co-ordination means which cause the position of afirst co-ordination axis K1, integral with first element 9a, to vary inrelation to a second co-ordination axis K2 integral with second element11b. Second co-ordination axis K2 is the axis of a pivoting connection28 which connects element 11b to the machine's framework. Co-ordinationaxis K2 is located at an equal distance from articulation axes A1 and A4of second element 11b and outside parallelogram A1, A2, A3, A4.

Co-ordination axis K1 is the articulation axis between element 9a and aneccentric trunnion 29 of a crank 31 pivoting around an axis J inrelation to the machine's framework. Co-ordination axis K1 is close toarticulation axis A2 by which first element 9a is articulated to thatsecond element 11a which is not connected to co-ordination axis K2. Axesof co-ordination K1 and K2 are perpendicular to faces 3a and 3b andconsequently parallel to the other axes A1-A4, C1-C4.

Considering Line M (FIG. 1) passing through rotation axis J of crank 31and co-ordination axis K2, the two minimum-volume positions of chamber17, which correspond to the extreme values for the angles of theparallelogram, are obtained when the first co-ordination axis K1 islocated on Line M, between axes K2 and J in FIG. 1, or beyond axis J inFIG. 5. In effect, it is in this position that the distance between axesK1 and K2 is the shortest and greatest respectively, and consequentlyangle Q1 is the smallest and largest respectively.

The radius of gyration of co-ordination axis K1, i.e. the distancebetween axes J and K1, is smaller than the distance betweenco-ordination axis K2 and articulation axis A1 between the two elements9a and 11b connected to co-ordination axes K1 and K2. Thus, therotations of crank 31 produce to and fro angular movements of secondelement 11b around pivoting connection 28.

The crank is designed so that the position of co-ordination axis K1, inthe first minimum-volume position (FIG. 5), corresponding to the startof combustion, is such that the volume of chamber 17 in this position isnot zero but by contrast corresponds to the compression ratio that wewish to give to the machine, and so that the position of co-ordinationaxis K1 in the second minimum-volume position or end of exhaustposition, shown in FIG. 1 is such that the volume of chamber 17 is zeroin this position. If we assume that the position of co-ordination axisK2 is defined, the direction of Line M passing through co-ordinationaxis K2 and the position of axis K1 being on first element 9a, the twoabove-mentioned conditions give the two positions of axis K1 on Line Mto achieve the two minimum-volume positions of chamber 17 andconsequently give the position of axis J located on Line M as being halfway between the two positions of K1.

In neither of the two minimum-volume positions (FIGS. 1 and 5), isarticulation axis A1 between the two elements 9a and 11b connected tomeans of co-ordination 28/31, located on Line M. Thus, in thesepositions the direction of pivoting of second element 11b aroundco-ordination axis K2 necessarily changes. If axes A1 and K1 were bothto pass onto Line M there would be indetermination as regards thedirection of rotation of second element 11b from this position.

However, in the first minimum-volume position (FIG. 5) corresponding tothe start of combustion, axis A1 is not far from Line M. Angle B whichseparates axes K1 and K2 seen from axis A1 is therefore almost 180°.Furthermore, the directions of rotation F and G of crank 31 and element11b respectively from this minimum-volume position are the same. Takingthese conditions into account, a relatively small angular displacementof crank 31 produces on second element 11b a relatively large angulardisplacement, more than proportional to the ratio of the gyration radiiof axes K1 and A1. Moreover, as axes K1 and K2 are both located outsidethe parallelogram, angle B is much greater than corresponding angle Q1,which is almost 120° in the example. Thus the angular travel to be madeby element 11b for the parallelogram to pass from the firstminimum-volume position (FIG. 5) to the subsequent maximum-volumeposition (FIG. 6) in which the parallelogram is a rectangle is about 30°and therefore relatively small. For two cumulative reasons, crank 31therefore need make only a relatively short angular travel for element11b to perform a rotation of about 30° around axis K2 which is necessaryfor parallelogram A1, A2, A3, A4 to become a rectangle and consequentlychamber 17 to achieve its maximum volume.

In the example shown, crank 31 need only make a rotation TD (FIG. 6) ofabout 75° for elements 9a, 9b, 11a, 11b to pass from the firstminimum-volume position (FIG. 5) to the following maximum-volumeposition in which parallelogram A1, A2, A3, A4 is a rectangle.

We can also see that in the situation in FIG. 7 corresponding to arotation of 90° of crank 31 starting from the first minimum-volumeposition, the rectangular configuration of parallelogram A1, A2, A3, A4is clearly exceeded, i.e. angle Q1 is already reduced to a value ofabout 75°.

This is advantageous because explosion of the gases may occur veryquickly, for a given speed of rotation of the crank, and this minimisesthe time during which the heat is dissipated through the metal walls,and consequently minimises heat loss.

The amplitude of the oscillating movement of second element 11b is onlyabout 90° between the two minimum-volume positions of chamber 17 shownin FIGS. 1 and 5. This is obtained by giving the gyration radius ofarticulation axis A1 around second co-ordination axis K2 a sufficientlylong length as compared to the gyration radius of co-ordination axis K1around axis J of crank 31.

FIG. 6 shows the maximum-volume situation of the chamber at the end ofexplosion, showing angle TD which was travelled through by co-ordinationaxis K1 since the first minimum-volume position (start of combustion),and angle TE, of about 105° which remains to be travelled until thesecond minimum-volume position, as well as the two angles UD and UEcovered by articulation axis A1 around co-ordination axis K2. Due to thegeometry selected, the two angles TD and TE, very different from eachother, produce for axis A1 two essentially equal angles of displacementUD and UE respectively.

In the first minimum volume position (FIG. 5) the pressure of the gasesacting on element 9a has a resultant P which acts on trunnion 29 ofcrank 31 in a direction which is essentially tangential in relation tothe circular trajectory of axis K1 of trunnion 29, and which is in thedirection of rotation F of crank 31. This resultant is therefore veryeffective for transmitting torque to crank 31 without producingparasitic stress in the mechanism. This is due to the small value ofangle V between longitudinal axis Da of element 9a, a direction to whichresultant P is essentially perpendicular, and Line M which correspondsin this position to the direction of the lever arm of crank 31. Anothercause of the favourable application of the force of the gases on crank31 is the suitable direction chosen for the rotation of crank 31. If adirection of rotation had been chosen for crank 31 which was opposite todirection F, operation would also have been possible since starting fromthe position in FIG. 5, chamber 17 would increase in volume just thesame to return to the situation shown in FIG. 4. But the transmission ofthe force to the crank would be in an extremely indirect manner by themedium of first element 9b, and second element 11b operating as areverser lever pulling element 9a towards the left in FIG. 5.

As shown in FIG. 3, crank 31 is connected to an output shaft 30 towhich, in a standard manner, an inertia flywheel may be connectedtogether with a multiple-ratio transmission device to form a power plantfor a motor vehicle. In an equally standard manner, this inertiaflywheel, and/or the inertial load constituted by the vehicle, providecrank 31 with the energy required to maintain operation during theenergy consumption stages (inlet, compression, exhaust).

Crank 31 has two eccentric trunnions 32, one for each elemental machine1, offset by 180° in relation to each other around axis J to cancel outthe main constituents of the inertia of each elemental machine 1. A moreperfect cancellation is achieved if the two elemental machines 1 arecompletely offset in relation to each other by 180° around axis J sothat all the movements in each elemental machine 1 are symmetrical withthose in the other elemental machine 1 in relation to axis J (ignoringthe axial offsetting of one machine in relation to the other along axisJ).

The machine shown in FIGS. 1 to 6 has means of adjustment enabling itsoperation to be optimised.

In particular, pivoting connection 28 has a trunnion 32 (FIG. 1) aroundwhich second element 11b pivots and which is supported by a cam 33mounted rotationally in the framework. When, as shown in FIG. 1, cam 33is positioned so that trunnion 32 is as close as possible to axis J ofcrank 31, angle B and consequently angle Q1 are as small as possible inthe first minimum-volume position of chamber 17 (FIG. 5). Consequently,the volume of cheer 17 in the first minimum-volume position is as largeas possible, which corresponds to the minimum compression ratio for themachine, since the maximum volume of chamber 17, defined by therectangular configuration of parallelogram A1, A2, A3, A4 (FIG. 6), isindependent of the position of trunnion 32.

In the second minimum-volume position (FIG. 1), this position oftrunnion 32 again corresponds to the smallest possible value for angleQ1 and consequently to the smallest possible volume for chamber 17, i.e.zero volume in the example.

If, as shown in FIGS. 8 and 9, cam 33 has turned through 180° so thattrunnion 32 is as far away as possible from axis J of crank 31, angle Q1in the first (FIG. 8) and second (FIG. 9) minimum-volume position hasincreased. This corresponds to a reduction in volume of chamber 17 inthe first minimum-volume position and consequently to an increase in thecompression ratio of the machine and to an increase in volume of chamber17 in a second-minimum volume position (FIG. 8). This relatively smallincrease may be regarded as a drawback since it gives rise to a deadvolume from which the exhaust gases cannot be expelled mechanically.

Adjustment in rotation of cam 33 in order to adjust the compressionratios of the machine may be performed manually, even during running, orautomatically. For example, cam 33 may be connected to a device thatmeasures depression in inlet 22 in order to increase the compressionratio when this depression is high (low absolute pressure) and to reducethe compression ratios when the absolute pressure in inlet 22 becomeshigher. Such automatic adjustment would be particularly advantageous inthe case of a supercharged engine.

As we know, it is advantageous to adjust the timing of a thermal engineto suit its operating parameters, particularly the speed of rotation andthe load.

This is enabled according to the invention, by rotating turret 8 aroundthe axis of central hole 24. In the diagram of the example, thisrotation is enabled by a pinion 34 engaging with teeth 36 on part of theperiphery of turret 8 (FIG. 3).

FIG. 7 shows that if, from the position shown, turret 8 had been turnedin the direction shown by arrows H, exhaust port 21 would have beenuncovered sooner by element 9a and consequently chamber 17 would havecommunicated earlier with the exhaust. This corresponds to a positionwhich is desirable when the engine's speed of rotation is higher. Thisangular offsetting also places inlet port 19 in a position in which itwill begin to communicate with chamber 17 slightly before the end of theexhaust stroke, which is also desirable for high speeds, particularlyif, as shown in FIG. 9, the volume of chamber 17 in the second minimum-volume position is not zero we thus achieve, in a known way, ascavenging effect on the last remaining burnt gases which are flushedtowards the exhaust port by fresh gases entering through the inlet port.

The angular position of turret 8 may be controlled manually orautomatically depending on the speed of rotation of crank 31 and thepressure at inlet 22. The precise adjustments to be made on the basis ofthese two parameters may be determined by the technician according tostandard knowledge. It should be noted, however, that due to the largegas flow cross-sections enabled by the invention, advancing the openingof the ports and retarding their closure is not as great as in standardengines with pistons and cylinders.

We shall not describe in further detail the means of cooling the engine,comprising for example various cavities 37 (FIG. 3) in intermediatepartition 6 and in heads 4, nor the means of lubricating the jointedcouplings.

FIG. 10 and the bottom of FIG. 3 show a simplified version capable ofoperating without a lubrication circuit due to a fuel supply comprisinga mixture of oil+petrol+air 38 penetrating through an inlet connection39 into a part 40 of the peripheral space located between elements 9a,11a, 9b, 11b and the inner face of peripheral wall 7 of housing 2. Inletport 19 comprises a blind cutaway section in face 3a, through whichchamber 17 communicates selectively, during the inlet stroke, withanother part 41 of the above-mentioned peripheral space.

Furthermore, the inner face of peripheral wall 7 is shaped so as to bealmost in contact with elements 9a-11b on one side close to articulationaxis A1 whose trajectory is circular around co-ordination axis K2, andon the other side close to the diametrically opposite axis A3 along partof the trajectory of the latter. As the volume of chamber 17 increasesduring the inlet stroke, these quasi contacts, forming a sealed barrier,separate areas 40 and 41 of the peripheral space from each other, andthe volume of area 41 decreases, which compresses the inlet gases andpushes them towards chamber 17 through port 19. This gives rise to asort of forced inlet, or even supercharging of chamber 17. We canappreciate the variation in volume of area 41 by comparing FIGS. 1(start of inlet) and 10 (inlet in progress).

FIGS. 5 and 7 show that, during compression and explosion, area 41 againincreases in volume and axis A3 moves some distance away from the innerperipheral face of peripheral wall 7, which enables area 41 to readmitgas from area 40.

According to the modified embodiment shown in FIG. 10 and at the bottomof FIG. 3, the air/petrol/oil mixture bathes the entire mechanismlocated in housing 2, which ensures lubrication without a separatelubrication circuit.

In the example shown in FIGS. 11 to 13, which will only be described asregards its differences as compared to the example shown in FIG. 10,first element 9b opposite that connected to the means of co-ordination(crank 31) rigidly supports two vanes 56, 57 each close to one of thearticulation axes A3, A4 of the said first element. The peripheral faceof inner peripheral wall 7 has two notches 58 and 59 whose profilecorresponds to the envelope of the end positions of vanes 56 and 57during the inlet stroke (FIG. 11: start of inlet, FIG. 12: end ofinlet).

Moreover, during the inlet stroke, the volume of area 41 of thehousing's peripheral space, located between the two vanes 56 and 57decreases very sharply. Its reduction in volume may, for example, be 650cm3 for an engine in which chamber 17 has a maximum volume of 400 cm3.Thus, element 9b forms with peripheral wall 7 of the housing amechanical engine-supercharger compressor.

Then, during the gas explosion stroke, vanes 56 and 57 are offset by thewalls of notches 58 and 59, which enables area 41 to readmit gas 38which has entered through connection 39 (as shown in FIG. 10).

If the direction of rotation of crank 31 were reversed, the vanes wouldhave to be placed on element 9a in order to create an area whose volumedecreases during the inlet stroke. But this would be less advantageoussince the bearings on crank 31 would have to be sealed.

In the example shown in FIGS. 14 and 15, face 3a is made completely onthe corresponding head 4 and the inlet 19 and exhaust 21 ports cantherefore no longer be adjusted around the axis of central hole 24. Face3a has a circular groove 42, for example centered around the axis ofhole 24. This groove is partly occupied by flat ring 43 with a radialslot 44. Ring 43 has an outer diameter which is essentially equal to theouter diameter of groove 42. Its axial thickness and radial width aresmaller than the axial depth and radial width of groove 42.

Furthermore, the position of groove 42, the diameter of its radiallyouter edge 42b and the radial width of ring 43 are selected so that thelines of proximity 46 between first elements 9a and 9b are locatedradially between radially outer edge 42b of groove 42 and radially inneredge 43a of ring 43, at least for the positions of crank 31 for whichchamber 17 must be isolated from the peripheral space surrounding theelements inside peripheral wall 7. Furthermore, elements 9a and 9b aredesigned, at least in the said positions of crank 31, to completelycover radially inner edge 43a of ring 43 except for those parts of thisedge which are facing chamber 17. In other words, edge 43a must not bevisible to an observer located in the peripheral space of the housing.Preferably, slot 44 should not appear in this space either.

Thus, the high pressure in chamber 17 penetrates into groove 42 and, onradially inner face 43a of ring 43, generates a thrust directed radiallyoutwards which presses ring 43 in an essentially sealed way againstradially outer edge 42b of groove 42, and, on back face 43b of ring 43generates a thrust directed axially towards elements 9a and 9b whichcreates a seal between ring 43 and these elements.

Slot 44 of ring 43 enables ring 43 to increase in diameter and pressagainst radially outer edge 42b under the pressure of the gases actingon its radially inner face 43a.

Since lines of proximity 46 between elements 9a and 9b are always facingring 43, ring 43 prevents the gases of chamber 17 from passing behindlines of proximity 46, and then into the peripheral space, escapingalong face 3a.

Furthermore, the axial thrust on ring 43 is transmitted by ring 43 toelements 9a and 9b and presses the latter against face 3b which createsa contact seal between face 3b and elements 9a and 9b. This prevents thegases from escaping from chamber 17 towards the peripheral space alongface 3b.

An elastic element such as a corrugated washer or the like, may beplaced between back face 43b of ring 43 and the bottom of groove 42 toachieve the initial pressure between ring 43 and elements 9a and 9b, andconsequently to prevent the gas from pressing ring 43 against the bottomof groove 42 instead of pressing it against elements 9a and 9b. Thetotal area of back face 43b of ring 43 is sufficiently large for theaxial force generated by the gas on ring 43 to be sufficient.

The example shown in FIG. 16 shall only be described as regards itsdifferences as compared to that shown in FIGS. 1 to 9.

First elements 9a and 9b are lengthened and offer each other threeconvex cylindrical surfaces S1, S2, S5 and S3, S4 and S6 respectively.Axes C5 and C6 of surfaces S5 and S6 intersect the same line L56 locatedat an equal distance between lines L14 and L23 and parallel to thelatter. Surfaces S5 and S6 thus form a pair of convex cylindrical wallswhich is located between pair S1, S4 and pair S2, S3 previouslydescribed.

Radius R5 and R6 of surfaces S5 and S6 is slightly smaller than radiiR1-R4, all of which are equal, of surfaces S1-S4. There is thus a slightclearance 47 between surfaces S5 and S6. This clearance presents noproblem since the two chambers 17 defined between elements 9a and 9b oneither side of clearance 47 are always at the same pressure and at thesame stage of the cycle of operation in all the angular positions ofcrank 31. Surfaces S5 and S6 can therefore be made without specialfinishing and in particular do not need to be made on inserts 16 such asthose on surfaces S1-S4.

It is thus possible to create very simply a machine of reduced sizewhose displacement capacity is double that of the one shown in FIGS. 1to 9.

Since the amplitude of the movements of chamber 17 closest toco-ordination axis K2 is smaller than that of the other chamber 17located on the right-hand side in FIG. 16, the inlet and exhaust portsmay be shaped and arranged slightly differently for each chamber (thisis not shown).

In the diagrams of the example shown in FIGS. 17 to 19, the assemblyformed by the four elements 9a, 9b, 11a and 11b is the same as in FIGS.1 to 9, with two convex cylindrical walls S1, S2 and S3, S4 respectivelyon each of first elements 9a and 9b. However, the means of dynamicsealing between the convex cylindrical walls of the same pair S1 and S4,and S2 and S3 respectively, instead of consisting of a mere proximity,comprise, for each pair, a Z-shaped floating bar 48 each base of whichends in a slightly re-entrant fin 49. The said floating bar is an easyapproximation to achieve as compared to a biconcave body which wouldhave two opposing concave cylindrical faces marrying up the two convexcylindrical walls such as S2 and S3 to seal off one from the other. Eachbar 48 is forced to center itself on corresponding Line L14 or L23 sincethe two areas of the bar located either side of this line are wider thanthe distance between the two cylindrical walls along this line.

Thus, each floating bar 48, which slides at the same time on bothcylindrical walls of the same pair, such as S2 and S3, so that it sealsoff one from the other, is always automatically positioned in a suitableway to ensure such sealing, whatever the attitude of the four elements9a, 9b, 11a and 11b in relation to each other.

As FIG. 19 shows, floating bars 48 have at each longitudinal end, in theextension of the bases of the Z, tongues 53 bent towards the inside ofchamber 17 to press in a sealed manner against faces 3a and 3b of thehousing.

The embodiment shown in FIGS. 17 to 19 also differs from that shown inFIGS. 1 to 9 in its means of co-ordination which comprise, in additionto crank 31 connected to the drive shaft (not shown) a second crank 51which is connected to crank 31 by two pinions 52 mounted in series sothat second crank 51 turns at the same speed and in the oppositedirection to crank 31.

Crank 31 drives in rotation first co-ordination axis K1, which in thisexample is confused with articulation axis A2. The second crank 51drives in rotation the second co-ordination axis K2 which, in thisexample, is confused with articulation axis A4 opposite axis A2.

Axes of co-ordination K1 and K2 are therefore symmetrical in relation tocenter W of parallelogram A1, A2, A3, A4 which coincides with the axisof hole 24 for the spark-plug. The assembly of the machine issymmetrical in relation to this center, including axes of rotation J1and J2 of cranks 31 and 51.

In FIG. 17, the machine is shown in a maximum-volume position of chamber17. The minimum-volume positions are achieved when axes K1 and K2 are onLine N intersecting axes J1 and J2.

In FIG. 18, the machine is shown close to such a minimum-volumeposition.

By choosing the appropriate distance between axes J1 and J2 of the twocranks 31 and 51 as well as the gyration radius of axes K1 and K2 aroundaxes J1 and J2, we define the distance between axes K1 and K2 in each ofthe two minimum-volume positions of chamber 17, and it is thus possible,as in the previous embodiments, for these two volumes to be different.

During operation, centre W of parallelogram A1, A2, A3, A4 isstationary. Consequently, the movements of the four elements 9a, 9b,11a, 11b are equivalent to to-and-fro movements of elements 9a and 9b inrelation to each other, with a correlative pivoting movement of elements11a and 11b, and a superimposed oscillating movement of the wholeassembly around the geometrical axis passing through centre W.

Excellent equilibrium can be achieved for all the inertial forcesgenerated by this combination of movements by providing a machine thatcomprises two elemental machines stacked one on top of the other(essentially as shown in FIG. 3) with an offset of 180° of angle ofcrank 31 between them.

In the example in FIGS. 17 to 19, as we have seen, sealing bars 48 arestationary in relation to Lines L14 and L23.

The embodiment shown in FIG. 20 exploits this observation. The secondelements are articulated to the first elements around the correspondingaxes of convex cylindrical walls S1-S4. In other words, axes A1 and C1,A4 and C4 are indistinguishable by pairs. In these conditions,longitudinal axis Ea or Eb of each second element 11a or 11b isindistinguishable from Line L23 or L14 respectively. Each dynamicsealing body 54 is therefore stationary in relation to one of the secondelements 11a and 11b. This has made it possible to create a rigidconnection between each sealing body 54 and the respective body ofsecond elements 11a and 11b. Each sealing body has a biconcave shapemarrying up the two convex cylindrical walls between which it createsdynamic sealing.

This makes it possible to create between each sealing body 54 and thetwo cylindrical walls with which it co-operates, a high-quality seal,suitable for instance for diesel cycle operation.

Furthermore, in the example in FIG. 20, co-ordination axes K1 and K2 areeach connected to one of the second elements 11a and 11b respectively,in symmetrical positions in relation to centre W of parallelogram A1,A2, A3, A4. Axes K1 and K2 are driven in rotation by two cranks such as31 and 51 in FIGS. 17 and 18 which are symmetrical in relation to centreW and connected to each other to turn in opposite directions.

Making the machines according to the invention is particularly simple,since the main operating surfaces can all be made flat or cylindrical.Sealing is achieved under zero or low load and wear of the machine istherefore reduced. The speed of relative displacement at the sealinglines or surfaces is remarkably low as compared to the speed of rotationof the crank. Furthermore, a given speed of rotation of the crank makesit possible to achieve twice as many cycles per unit of time than aconventional piston and cylinder engine. It is therefore possible toenvisage speeds of rotation double those of conventional engines, withconsequently four times as many cycles per unit of time. At such cyclespeeds, the combustion and explosion strokes are very brief and heatloss is particularly low. For a given power, the speed doubles anddoubling the number of cycles per revolution of the crank in theorymakes it possible to have a cubic capacity ("cc") four times smaller,which limits the surfaces from which heat escapes and consequentlyfurther limits heat loss.

It will also be noted that the movement of first and second elements 9a,9b, 11a, 11b against faces 3a and 3b is a turning movement without abreak point, which is particularly favourable for achieving perfectrunning in on these surfaces, making the surfaces in questionparticularly resistant to wear and exhibit particularly good sealingqualities by simple proximity. The large contact surface betweenelements 9a and 9b and faces 3a and 3b promotes cooling of elements 9aand 9b.

In the example shown in FIGS. 21 to 24, the cylindrical walls S1 to S4are defined by shells 61 which, in each pair, are directly pushedagainst each other along a sealing line 60 forming one of the ends ofchamber 17. Each shell has a free inner edge 62 always located insidechamber 17 and an outer edge 63 always located outside chamber 17. Outeredge 63 is adjacent to a fixing area 64 of shell 61. Area 64, alwayssituated outside chamber 17, is fixed in a sealed manner to firstelement 9a or 9b to which it is associated. Each first element thereforehas two shells 61, directed towards each other from their respectivefixing area 64.

Starting from fixing area 64, shell 61, made of steel for example,floats by elastic bending. The fact that it presses against the othershell 61 of the same pair is due to elastic prestressing duringassembly.

Behind each shell 61 is an intercalary space 66 which communicates withchamber 17 through a slot 67 adjacent to inner edge 62 of the shell.Thus, when chamber 17 is full of gas under pressure, this gas passesinto intercalary space 66 to strengthen the mutual pressing of the twoshells 61 of each pair. The back faces of shells 61 are permanentlyexposed along their entire length to the pressure of chamber 17. Bycontrast, their front faces, i.e. cylindrical walls S1 to S4, are notexposed to the pressure of chamber 17 except along a reduced andvariable length. Thus, when chamber 17 has one or other of its twopossible minimum volumes (FIG. 22), one of the cylindrical walls (S1) ofeach pair is exposed along practically its entire length to the pressurein chamber 17 whilst the other cylindrical wall (S4) is only exposed tothe pressure along a short part of its length. Thus, the pressing forceacting on this wall S4 compensates only partially for the pressing forceacting on the front face of associated shell 61, which therefore presseshard against the other shell. The latter does not bend unduly since thepressing occurs close to its fixing area 64, and thus with a smallbending torque.

By contrast in a situation not shown here, where the volume of thechamber is essentially at its maximum, the force produced by thepressure is more or less the same on both shells so they thereforebalance each other out with a very slight deformation as compared to theneutral state. The deformation of the shells is thus reduced in allcases.

As shown in FIG. 24, each shell 61 has along each face 3a or 3b a sideedge formed by a ridge 68 defined by the corresponding cylindrical wall,such as S3, and a chamfered wall 69 forming an angle of about 45° withcylindrical wall S3. When shell 61 undergoes bending movements, inneredge 62 and ridges 68, as well as the cylindrical wall that theysurround, move in relation to the body of the first correspondingelement. Ridge 68 is in movable proximity and essentially sealed withadjacent face 3a or 3b. Thus, the gas in intercalary space 66 cannoteasily escape in the way shown by arrow 70 in FIG. 22.

As FIG. 24 shows, each connecting wall 18 is integral with the body ofthe element (9a) that supports it. It is also terminated by two sideridges 71 but these ridges 71 are at a certain distance from faces 3aand 3b to avoid any friction.

On the side opposite each ridge 68, intercalary space 66 is limited by asealing segment 72 (FIG. 24) which is made to press in a movable andsealing manner against adjacent face 3a or 3b by a prestressed spring73. Each segment 72 has a chamfered face 74 which is parallel tochamfered face 69 of shell 61 although at a certain distance from thelatter. This chamfered face 74, as well as a side face 76 and a backface 77 of each segment, undergo the pressure existing in intercalaryspace 66, which thus helps to press segment 72 against the opposite face3a or 3b and against a pressing face 78 of the body of the correspondingelement, 9b in FIG. 24. This double sealed pressing prevents the gasunder pressure from escaping through an area 79 located between the bodyof first element 9a or 9b and each opposite face 3a or 3b.

As FIG. 23 also shows, each segment 72 and associated spring 73 extendcontinuously between the two fixing areas 64 of the two shells 61associated with corresponding element 9a or 9b. Spring 73 may be in theform of a corrugated elastic rod. Behind connecting wall 18, element 9aor 9b has opposite each face 3a or 3b a shaped groove 80 housing thecorresponding part of the length of segment 72 and spring 73. Thisgroove 80 communicates with chamber 17 through slots 67 between which itextends and also through the gap existing between ridges 71 (FIG. 24)and faces 3a and 3b. Thus, in this area too, the pressure pushessegments 72 against faces 3a and 3b and against pressing face 78 ofelements 9a and 9b. Between chamber 17 and areas 79 there is thuscontinuity of seal along the entire length of first elements 9a and 9bwhich is apt to be exposed to pressure.

In practice, in the vicinity of the fixing area 64 of each shell 61,priority would be given to encouraging reliability and reducing frictionrather than achieving a perfect seal since the escape paths leading tothis area are very complex and narrow, like labyrinths, and in any caseallow only a very small flow through. It is moreover possible toincrease this labyrinth effect further by roughening the faces definingintercalary spaces 66.

The embodiment which has just been described has the advantage ofachieving controlled sealing conditions between cylindrical walls S1 toS4 in a manner largely independent of the state of wear of the engineand precision of machining of the component parts. Furthermore, shells61 dampen the vibrations of the first elements in relation to each otherand prevent these vibrations from producing knocking between cylindricalsurfaces S1 to S4. This greatly prolongs the operating life of thesesurfaces and helps to keep, over time, the sealing quality along lines60 at a high standard.

In the embodiment shown in FIG. 25, segments 81 have been added alongthe side edges of shells 61 to further reduce the possibility of leakagealong a path such as that illustrated by arrow 70 in FIG. 22. Segment 72runs along the entire length of each first element 9a or 9b, asdescribed with reference to FIGS. 21 to 24. Thus, as shown at the bottomof FIG. 26, along each face 3a or 3b, intercalary space 66 is definedbetween the two segments 72 and 81. The pressure of the gases, assistedby a pre-stressed distancing spring 82, tends to keep the two segmentsapart and push them in a sealed way against face 78 of the body of firstelement 9b and against a sealing face 83 at the back of shell 61respectively.

Furthermore, the pressure, assisted by a prestressed spring 84 similarto spring 73, permanently pushes segment 81 against the correspondingopposite face, 3b in FIG. 26. Along connecting wall 18 (top of FIG. 26),there is only one segment (72). It is pushed by the pressure of thegases and prestressed by springs 73 and 82 as described above.

Of course, the invention is in no way restricted to the examplesdescribed and illustrated.

In the example shown in FIG. 1, axis K1 and/or axis K2 could be made tocoincide with one and/or other of articulation axes A1-A4.

With reference to the top of FIG. 3, distribution ports 19 and 21 couldbe made through face 3b, for example in a fixed position, and pivotingturret 8 could be replaced by a non-rotating plate having the solefunction of pressing against elements 9a and 9b under the action of thepressure in back-pressure space 26.

In the embodiment shown in FIGS. 14 and 15, groove 42 and ring 43 couldbe located in face 3b in order to make ports 19 and 21 through face 3amore easily, particularly if the inlet port is required to be a cutawaysection such as that shown in FIG. 10, which would then be made in face3a only.

In the embodiment shown in FIGS. 17 to 19, their is no necessity tocombine floating bars 48 on the one hand and the means of co-ordinationin the form of two crankshafts 31 and 51 on the other: these twoimprovements could be used independently of each other.

Similarly, in the example shown in FIG. 20, the means of co-ordinationcould be different.

The invention could be used to create a compressor or a pump or even anexpansion machine operating at two cycles per revolution, or even atwo-stroke engine operating at two cycles per revolution. In thesevarious cases, arrangements would generally be made for the twominimum-volume positions to correspond to identical volumes, so that thetwo cycles of each revolution of the crank would be identical.

I claim:
 1. A positive-displacement machine comprising, between twoflat, parallel faces facing one another (3a, 3b), two first opposingelements (9a, 9b) articulated to two second opposing elements (11a, 11b)around four articulation axes (A1-A4) perpendicular to the said faces(3a, 3b) and arranged at the four apexes of a parallelogram, each side(Da, Db, Ea, Eb) of which constitutes the longitudinal axis of one ofthe respective first and second elements, the elements supporting fourconvex cylindrical walls (S1-S4) which between them define avariable-volume chamber (17), the longitudinal axis (Da, Db) of eachfirst element (9a, 9b) being intersected by the axes (C1, C2; C3, C4) oftwo respective convex cylindrical walls (S1, S2; S3, S4), two lines(L14, L23) running in the same direction as the axes (Ea, Eb) of saidsecond elements (11a, 11b) each being intersected by the axes (C1, C4;C2, C3) of two respective ones of said convex cylindrical walls (S1, S4;S2, S3), the machine also comprising means of co-ordination (28, 31)connected to two of the elements (9a, 11b) along two co-ordination axes(K1, K2), the means of co-ordination comprising a crank (31) type systemconnected to a drive shaft and one (9a) of these two elements to makethe parallelogram oscillate between said flat faces (3a, 3b) and at thesame time cause its angles at the apex and consequently the volume ofsaid chamber (17) to vary, distribution ports (19, 21) being located onone at least of said opposing flat faces (3a) to cause said chamber (17)to communicate selectively with an inlet (22) and an exhaust (23)depending on the angular position of said crank (31), characterised inthat each first element (9a, 9b) rigidly supports the two convexcylindrical walls whose axes (C1-C4) intersect the longitudinal axis(Da, Db) of the said first element, in that each convex cylindrical wallforms with the convex cylindrical wall whose axis intersects the sameline (L14, L23) a pair (S1, S4; S2, S3) of cylindrical walls belongingto different ones of said first elements (9a, 9b), in that each firstelement has closure means extending between its two convex cylindricalwalls, and in that the machine comprises means of dynamic sealingbetween the convex cylindrical walls (S1, S4; S2, S3) of a same pair. 2.Machine according to claim 1, characterised in that the means of dynamicsealing comprise a proximity relation between the cylindrical walls of asame pair.
 3. Machine according to claim 1, characterised in that themeans of dynamic sealing comprise a floating body (48) mounted betweenthe cylindrical walls (S1, S4; S2, S3) of a same pair.
 4. Machineaccording to claim 3, characterised in that said floating body (48) is aZ-shaped floating bar.
 5. Machine according to claim 1, characterised inthat the means of dynamic sealing comprise, for each second element, anintermediate body (54) with two faces that are each in sealed contactwith one of the cylindrical walls (S1, S4; S2, S3) of a same pair. 6.Machine according to claim 1, characterised in that the closure meanspresent towards the chamber a concave-shaped face (18) which isessentially complementary to that of said cylindrical walls (S1, S2, S3,S4).
 7. Machine according to claim 1, characterised in that the axes(C1-C4) of said convex cylindrical walls (S1-S4) coincide with thearticulation axes (A1-A4) between the elements.
 8. Machine according toclaim 7, characterised in that the means of dynamic sealing (54) aresupported by the second elements (11a, 11b).
 9. Machine according toclaim 1, characterised in that the axes (C1-C4) of said convexcylindrical walls (S1-S4) are, on each longitudinal axis of firstelement (9a, 9b), located between the two articulation axes (A1, A2; A3,A4) intersecting the said longitudinal axis (Da, Db).
 10. Machineaccording to claim 1, characterised in that at least part of saiddistribution ports (19, 21) have an adjustable position in relation to aframework of the machine.
 11. Machine according to claim 10,characterised in that said ports (19, 21) are made through a turret (8)which is adjustable by rotation and whose outer periphery surrounds saidchamber (17) in all the angular positions of said crank (31). 12.Machine according to claim 1, characterised by means to cause thechamber to communicate with a back face of a plate (8) whose front faceconstitutes at least a part (3c) of one (3a) of the opposing faces, thisplate having an independence in relation to the framework which enablessaid plate to press against said first elements (9a, 9b).
 13. Machineaccording to claim 1, characterised in that one of the opposing faces,supported by a housing wall of the machine, has an annular groove (42)partially filled by a split ring (43), which is exposed to receive fromthe gases pressing forces directed towards said first elements (9a, 9b)and radially towards an outer peripheral edge (42b) of said groove (42),and which is capable of pressing in a sealed manner against the elementsand against the said outer peripheral edge under the action of the saidpressing forces.
 14. Machine according to claim 1, characterised in thatat least one of said cylindrical walls (S1-S4) is defined by a shell(61) which is elastically stressed towards the other cylindrical wall ofthe same pair, and in that a space (66) behind said shell (61)communicates with said chamber (17) so that the shell is furtherstressed towards the other cylindrical wall of the same pair by thepressure of the gases in the chamber.
 15. Machine according to claim 14,characterised in that said shell (61) is fixed in an essentially sealedmanner to one of said first elements (9a, 9b) in an outer area (64)which is always located outside said chamber (17) and in that an inneredge (62) of said shell (61), which is always located inside saidchamber (17), as well as two side edges (68) of the shell, have freedomof movement by bending of the shell.
 16. Machine according to claim 14,characterised in that each first element (9a, 9b) has, facing eachopposing face (3a, 3b), sealing means (72, 81) which are placed underpressure by the gases occupying said space (66) behind said shell (61).17. Machine according to claim 16, characterised in that the sealingmeans comprise, facing each opposing face, a sealing organ (72)extending the entire length of the chamber between two opposing fixingareas (64) belonging to two shells (61) defining two cylindrical walls(S1, S2; S3, S4) of a same first element (9a, 9b).
 18. Machine accordingto claim 16, characterised in that the sealing means comprise a sealingorgan (81) running along each side edge of each shell (61).
 19. Machineaccording to claim 14, characterised in that side edges (68) of saidshell (61) are at least approximately sealed with said opposing faces(3a, 3b).
 20. Machine according to claim 14, characterised in that thetwo cylindrical walls (S1, S4; S2, S3) of at least one of the pairscomprise two similar shells (61).
 21. Machine according to claim 1,characterised in that the closure means between the two convexcylindrical walls of each first element (9a, 9b) present towards theother first element a corrugated wall defining at least one projection(S5, S6) between the two cylindrical walls.
 22. Machine according toclaim 21, characterised in that the projection is a third convexcylindrical wall (S5, S6) resembling the other two.
 23. Machineaccording to claim 1, operating as a four-stroke thermal engine,characterised in that it comprises means to initiate combustion (25)positioned to correspond with said chamber (17) at least when the latteris in a first minimum-volume position.
 24. Machine according to claim23, characterised in that said co-ordination axes (K1, K2) are locatedoutside said parallelogram (A1, A2, A3, A4).
 25. Machine according toclaim 23, characterised in that the means of co-ordination are connectedto the elements so that the angular distance (TD) between two crankpositions corresponding to the first minimum-volume position and a firstmaximum-volume position respectively, is less than 90°.
 26. Machineaccording to claim 23, characterised in that the means of co-ordinationare designed and connected to the elements so that the volume of saidchamber (17) is greater in the first minimum-volume position than in asecond minimum-volume position, created at the end of an exhaust strokeduring which said chamber (17) communicates with an exhaust port (21)forming part of said distribution ports (19, 21).
 27. Machine accordingto claim 26, characterised in that in the second minimum-volumeposition, the volume of said chamber (17) is essentially zero. 28.Machine according to claim 22, characterised in that the distributionports comprise an inlet port (19) consisting in a cutaway section madein at least one of said flat faces (3a, 3b) in order to cause chamber(17) to communicate selectively with a supply space (41) located alongat least one part of the outer periphery of elements (9a, 9b, 11a, 11b),in a housing (2) surrounding the elements, this space being connected tomeans of combustion gas supply.
 29. Machine according to claim 28,characterised in that said supply space (41) is delimited between twobarriers (56, 57) which are spaced apart in the peripheral direction ofthe housing and create, at least during an inlet stroke, a quasi sealbetween the inner profile of the housing and the elements, in an area ofthe periphery of the housing which is selected so that supply space (41)reduces in volume when it communicates with said chamber (17). 30.Machine according to claim 29, characterised in that the housing has aninner profile having certain areas (58, 59) which correspond essentiallyto the envelope of the positions of two areas of the elements betweenwhich areas said supply space (41) is delimited, the two barriers beingcreated by proximity between the two areas of the elements and the innerprofile of the housing.
 31. Machine according to claim 29, characterisedin that the two areas of the elements are integral with a same saidelement (9b), and in that the barriers have at least one vane (56, 57)integral with this element or the housing, and a notch in the housing oron the said element respectively, the said notch having a profilecorresponding to the envelope of the end positions of the vane inrelation to the notch.
 32. Machine according to claim 28, characterisedin that the barriers separate the supply space from an inlet space (40)with which said supply means (39) communicate.
 33. Machine according toclaim 30, characterised in that the supply means are means of supplyingan air/petrol/oil mixture.
 34. Machine according to claim 24,characterised in that said crank (31) is arranged so that in the firstminimum-volume position the lever arm of the crank is positionedtransversely to the direction of the force of expansion (P) of the gasacting on that one (9a) of the two elements which is connected to saidcrank (31), and said lever arm moves in the direction (F) of the saidforce (P).
 35. Machine according to claim 1, characterised in that themeans of co-ordination (28) can be adjusted to change the volume of thechamber in one of the minimum-volume positions, and thus adjust acompression ratio of the machine.
 36. Machine according to claim 1,characterised in that the means of co-ordination comprise, apart fromthe system of a crank (31) type connected to one (9a) of the two saidelements along a first one of said co-ordination axes, a pivotingconnection (28) between the other (11b) of the two elements and amachine framework around a second one of said co-ordination axes (K2).37. Machine according to claim 36, characterised in that the twoelements to which the means of co-ordination are connected are a first(9a) and one of the second elements (11b), and in that the distancebetween the second co-ordination axis (K2) and articulation axis (A1)between the two elements (9a, 11b) is greater than the radius of thecrank.
 38. Machine according to claim 37, characterised in that thedistance between said second co-ordination axis (K2) and axis (J) ofsaid crank (31) is slightly shorter than the sum of the distancesseparating the articulation axis (A1) of the two elements from thesecond co-ordination axis (K2) on the one hand and from the axis (J) ofthe crank on the other hand.
 39. Machine according to claim 38,characterised in that in the first minimum-volume position, articulationaxis (A1) between the two elements (9a, 11b) is located between the twoco-ordination axes (K1, K2).
 40. Machine according to claim 36,characterised by comprising means for adjusting the distance between thesecond co-ordination axis (K2) and the crank pivoting axis (J) inrelation to the framework.
 41. Machine according to claim 1,characterised in that the means of co-ordination comprise two crank typesystems (31, 51), each connected to one of the said two elements. 42.Machine according to claim 41, characterised in that the said twoelements are two opposing elements (11a, 11b).
 43. Machine according toclaim 41, characterised in that the two crank type systems areessentially identical (31, 51), connected together in order to turn atthe same speed in opposite directions, and, like said co-ordination axes(K1, K2), are symmetrical in relation to centre (W) of theparallelogram.